Grinding process and apparatus



May 14, 1940v y J. CRn-Es 2,200,822

GINDING PROCESS AND APPARATUS Filed Oct. 15, 1957 2 Sheets-Sheet 1 orngys.

May 14 1940- l J. cRrrEs 2.200.822

GRINDING PROCESS AND APPARATUS Filed 001i. 15, 1957 2 Sheets-Sheet 2 if @www Patented M., 111, 1940 PATENT oFElcE" azoaazz GaTNmNG-Pnoonss AND APPARATUS Joe Crites, Evanston, Ill., asslxnor to Combustion Engineering Company, Inc., New York, N. Y., a corporation of Delaware Application october 15, 1937, semi No. 16am o claims.

This invention relates to a new and improved grinding process and apparatus, and relates moreparticularly to an improved method and means for facilitating the grinding or pulverizing of nely divided material.

. In one well known grinding system, the material to be ground or pulverized is introduced into a mill comprising rotating rollers or hammers, and an airstream passed through the mill carries out material sumciently ground to be capable of suspension in the air stream. This air stream is *then passed through a separator wherein the insufllciently pulverized material is rejected (and usually returned to the mill for further grinding)4 the air stream carrying out only the sufliciently pulverized materialwhich is subsequently separated from the stream. The insumciently pulverized material which is rejected by the air stream and returned to the mill is often o f such a .ne grade that itcannot be emciently handled by the mill. In the case of a hammer mill, the hammers can exert but little impact on a ilne particle because of the inertia of the ne particle and because the windage from the hammers blows the fine particles out of the path of the hammer. In a roller mill diiiiculty is encountered because the finely pulverized materials ow like water and are carried out of the path of the rollers by the air currents set up within the mill. l

The broad principle of the present invention consists in withdrawing these une tailings or insuiilciently pulverized material whichare rejected by the separator and mixing these materials with a small quantity! of water or other temporary binding agent'thus forming a paste or other conglomerate having sumcient bulk to resist the air currents within the mill, this mixture being returned to the mill for further treatment between the grinding elements. The air stream passed through the mill is heated so that the Water or other temporary binding agent will be evaporated and withdrawn by the air stream as the materials in the mixture thus introduced are pulverized.

The principal object of this invention is to provide an improved process and apparatus for grind- Ving line materials as hereinabove briefly described and disclosed more in detail in the specifications which follow.

Another object is to' provide an improved process for increasing the bulk-'and facilitating the handling of fine materials during a grinding operation.

Another object is to provide improved means for selectivelywithdrawing materials of various grades from a grinding and separating apparatus.

y Other objects and advantages of this invention will be more apparent from the following detailed description of one approved form of apparatus designed and operating according. to the principles of this invention.

In the accompanying drawings:

Fig. 1 is a central vertical section (with parts shown in elevation) of the assembled grinding and separating apparatus.

Fig. 2 is a horizontal section, on a somewhat larger scale, substantially on the line 2-2 of Fig. 1.

Fig. 3 is a partial horizontal section taken sub. stantially on the line 3-3 of Fig. 1.

, Fig. i is a partial elevation, looking from the right at the apparatus shown in Fig. 3.

, The apparatus comprises, in general, a closed upright continuous casing in the lower portion of which is located the grinding mechanism A, and in the upper portion of which is located the separating apparatus B. At C is indicated means for feeding material to be ground or pulverized to the mill A, while at D is indicated means for feeding heated air or other gases to the mill, the air stream owing upwardly through the mill and separator B and out through conduit E with sumciently pulverized material in suspension. A means F positioned intermediate the separator and. mill is adapted to collect the heavier tailings rejected by the separator, and at G, G' and G" are indicated means for withdrawing rejected material from different portions of the assembly and delivering this material into a mixer H to form the paste or conglomerate that is delivered back into the mill A for further treatment. 35

The enclosing upright housing or casing which is preferably centered about the central vertical axis a: comprises a lower cylindrical portion I in which milla. is housed, an upper cylindrical portion 2 of somewhat greater diameter which houses the separator mechanism B, and an intermediate upwardly expanding conical portion 3.

The mill A, in the example here shown, is ofthe well known rollertype and comprises the central vertical drive shaft 4 journaled in suitable bearings and rotated through bevel gearing 5 from the drive shaft 6. The spider 'l carried at the upper end of shaft 4 supports a circular seriesofr'ollercarriers B each pivoted in the'spider so that the grinding rollers 9 supported by the carriers 8 may swing radially outward from the central axis :c under the llniuence of centrifugal force as the spider is rotated. The rollers 9 are freely rotated about their own axes and as they swing' outwardly will engage the stationary bull-ring ill and roll 55 thereon. The material to be ground is delivered intothe mill housing by any suitable means such las the pocketed feeder shown at II and comprising a portion of the feeding assembly C, this material falling downwardly between the grinding rollers 9 and bull-ring I0 so as to be crushed or pulverized therebetween. The air-supplying means D comprises a conduit I2 leading from any suitable source of heated air or otherv gases into the annular manifold I3 surrounding the mill. The air stream delivered from manifold I3 flows upwardly through casing I carrying in suspension material that has been suillciently finely divided by the mill to be capable of Such otation.

The separator B is preferably of the general type disclosed in the copending application of Joe Crites, Serial No. 132,784, led March 24, 1937. which became Patent No. 2,169,680 on August 15, 1939, and comprises a pairl of similar separating assemblies K and K' with an intermediate centrifugal sorting zone I4. These two separating assemblies K and K' are similar to one another and each comprises a central rotary element or whizzer" journaled for rotation about the central axis a: and consisting of a central disk or deector I5 from which projects outwardly a circular series ofV substantially radial vanes I6, these vanes being positioned vertically so as to present a minimum of obstruction to the upwardly flowing air stream. This rotary whizzer is carried by a vertical shaft I1 journaled in gear casing I8 supported from the outer casing 3 by a plurality of radially extending plates I9. The Whizzers are rotated by any suitable means, preferably a motor connected through horizontal motor shaft 2| and bevel gearing 22 journaled in gear casing I8 with the lower end of vertical whizzer shaft I1. 'Ihe outer ends of vanes I8 are beveled inwardly and upwardly and rotate in close proximity to the lower surface of a downwardly and outwardly projecting annular conical deflector 23 carried by casing 2. The supporting means comprises an annular inwardly projecting plate 24 which extends as a shelf over the upper outer end portions of vanes I8; 'I'he upper end of the outer peripheral casing 2 is closed by a cover plate 25 from the central portion of which projects the outlet conduit E. The air flow through the apparatus is preferably created and maintained by an-exhaust fan or blower which draws air upwardly and outwardly through the conduit E. It will be understood that only sumciently pulverized material is carried in suspension through this outlet conduit which leads into a suitable cyclone separator or other means for depositing the pulverized material from the air stream.

It will be noted that the only passage for this air stream through the separating assembly K is through the annular space between the central disk or deflector I5 and the outer stationary annulardeilector 23, and between the rapidly rotating vanes I6 which cut across this annular space. Only `the very finely divided particles of material held in suspension in the air stream will find their way upwardly between these vanes. I'he greater portion of the material above a certain size will be thrown outwardly against the stationary deiiector 23 and thence directed downwardly through casing 3. The portion of the air stream in the intermediate classifying zone I4 between the two separating assemblies K and K' will becaused to rotate by the rotary whizzers above and below this space so that the larger and heavier particles of material in the air stream which have passed separator K will be thrown outwardly into the peripheral portion 28 of this zone adjacent the enclosing wall 2. The material which passes separating zone I4 will have to pass through the upper separating assembly K' in which another separating action, similar to that performed by the lower separator K, will take place.` A last centrifugal sorting'operation will -be performed on the whirling air stream which passes the upper separator K' so that the heavier particles of material which have passed the two separating assemblies will be concentrated in the outer portion 28 of the upper centrifugal sorting zone 21. It will thus be seen that only the most nely divided and pulverized material will eventually be carried out in suspension in the air stream through outlet conduit E. The iineness of this delivered material may be varied, within certain limits, by changing the speed of rotation of the rotary whizzer, and consequently a variable speed driving means is preferred. 'I'his may be accomplished by using a variable speed motor 20 or by inserting suitable change-speed mechanism between the motor and the shafts l driven thereby.

The material rejected in the outer zone 28 of upper sorting space 21 will collect upon the upper shelf 24' and gradually nd its way back between the rotating vanes of whizzer K so that it will join the material rejected by whizzer K and the material separated by centrifugal sorting action in the outer portion 26 of the intermediate zone I4 and all of this material will be deposited on the lower shelf 24 and work it way back through the lower whizzer. This material, together with the material initially rejected by thel lower whizzer and thrown downwardly by deflector 23 will settle downwardly toward themill A.

The centrally positioned deflector and collec tion receptacle F is preferably supported for ro tation on the upper end of mill shaft 4. This deector is preferably dished upwardly or saucershaped and its outer peripheral edge is spaced fromr the adjacent inner wall of casing I so as to provide an annular air space 29 throughwhich the upwardly flowing air stream is forced to pass. This upwardly flowing air stream with its suspended material is rotating or whirling due to the motion imparted thereby by mill A and deflector F and will tend to follow the inner wall of casings I and 3 as it moves upwardly toward the separatorK. As a consequence, the material rejected by the separators tends to settle downwardly through the central quieter portion of the enclosure which is less agitated and where the upward air velocity is lowest. This material will for the most part be collected on or in the deecting receptacle F. This material will unavoidably contain, along with the properly rejected or oversized material, a considerable amount of already sulciently pulverized material which can eventually pass through the separators without further grinding treatment. As the material collected on deflector F is thrown outwardly by centrifugal force this finer material will be caught up by the air stream flowing upwardly through passage 29 and will eventually pass through the separators. This material returned from deflector F increases the saturation of the air stream at the separator and consequently increases the eiliciency of the separator. the return of this already suilciently pulverized material to mill A, the capacity of the mill for handling new material is increased. 'Ihe larger and heavier material collected on receptacle F is'not sufficiently pulverized andneeds further grinding treatment is, however, already so iinely divided that it is very easily deflected or carried away by the. air current setup within the mill and nds-its way with diillculty. back becasing I.

cylinder so as to be presented at the most desirvside of plate 3l.

tween the grinding elements 3. and III. This fine material tends to float away or be blown out of the path of the rollers, and similar diiiiculties will be encountered with other types of grinding apparatus such as a hammer or impact mill\.\

According to the present invention, the inaterial rejected by the separator is withdrawn from the mill-separator assembly and mixed with a small quantity of water or some other temporary binding agent so as to formv a paste or .conglomerate'mixture of larger and heavier units that may be more readily lreturned to the mill and delivered to the grinding elements for further treatment.

.The withdrawing mechanism G comprises a throw-outpocket 30 carried by a supporting plate 3| removably secured over an opening 32 in one side of mill-casing l. In the example here shown a pair of bolts 33 secured in ears 34 projecting from one side of plate 3| (see Figs. 3 and 4) are pivotally mounted at 35 in ears 36 projecting from A similar pair of bolts 31 pivoted at 38 in ears 39 on the casing engage in slots 4D formed in ears 4| projecting from the opposite By loosening the nuts i2 on bolts 31, these bolts may be swung out of slots 40 after which the plate or door 3l can be swung away from the casing about the hinge axis 315. This will permit access to the interior. of the casing. The throw-out pocket 30,in the form of a substantially closed casing, is mounted `on the outside of plate 3l. A substantially semicylindrical scoop 4 3 is secured at its outer end to a plate 44.1nounted for rotary adjustment by means of bolts 45 secured in one side wall of casing 30 and projecting through slots 66 in plate 44. 'Ihis adjustment permits the scoop to be rotated around the central longitudinal axis of the able angle to the air stream Within casing l. This scoop 43 projects inwardly through a suitable opening in supporting plate 3l so that the inner end of the scoop is positioned adjacent the peripheral edge of rotary deflector or receptacle F. Preferably the scoop projects inwardly at an angle opposed to the direction of rotation of the whirling materials within the casing, this direction being indicated by the arrow in Fig. 3.

A scraper 41 may be secured at 48 to the inner end portion of scoop 43, this scraper projecting inwardly over the outer upper surface of deilector F in position to scrape or dislodge matefrials therefrom.

The lower portion of the pocket o r casing 30 is in the form of a chute 49 leading into conduit 50 through which the collected materials are The collecting means G' comprises 'a conduit.'

51 which leads from an opening formed in the peripheral wall 2 of the separator casing where this wall surrounds the intermediate centrifugal sorting space .|4. The upper entrance end of conduit 51 may be closed by a door or damper able along the arcuate guide plate 6I. The door 58 is curvedv to conform with the curvature of wall 2 and when in the inoperative position shown in solid unes in Fig. 2 win form substanuany 'a' continuation of this wall. Just below the swinging door lith-a sector shaped plate or shelf 82 withdrawn through conduit 51. However, if door 58 is adjusted inwardly to some such position as shown in dotted lines it will servev as a scoop to `collect material (above .and upon the shelf .62) and direct this material into the Vconduit 51 and thence downwardly into mixer H-into which this conduit discharges. 'I'he percentage of material' withdrawn in this manner may be adjusted by changing the position of scoop 58 by means of adjustable handle 60. y I

The collecting means GV is substantially the same in all respects as the means G and includes a conduit 63also discharging into mixer H. The collecting means G communicates with the centrifugal sorting space 21 above the upper whizzer assembly K'.

It will now be apparent that any one or all of the collecting means G, G' or G may be used to withdraw material of various grades from diiferent parts of the mill-separator assembly. The ccarsest tailings will be withdrawn through apparatus G, and the finest rejected material through Aapparatus G.

discharge into the mixer conduit -or casing 66,

and any suitable means is provided for sprinkling or admitting water into the mixer. This waterfeed means is here shown as a pipe 68 provided with a control valve 69. The'conveyor B4 is preferably of the cutnight type as shown so that the tailings and water or other suitable temporary binding agent will be thoroughly mixed and slowly advanced toward the discharge end 19 of the mixer from which they are delivered into the mill housing so as to fall between the grinding elements 9 and l0. It will be understood that only suiicient water or other agent is added to temporarily bind the ne tailing particles together so as to form either a paste or a. loose conglomerate having suicient bulk and weightto resist the air .currents within the mill so that the material will be readily delivered between the relatively rotatable grinding elements.

By simply heating the air stream delivered into the mill to a suiiiciently high temperature, the water will be evaporated as the grinding process is performed so that the finely pulverized material particles will be again released for separate notation in the air stream.

Instead of utilizing a mixer H of the general type here shown, the Withdrawn tailings could al- C or a separate feeder as may be found desirable. K

I claim: 1. In combination, a mill comprising relatively .moving grinding elements, means for feeding dry material to be ground into the mill, a separator above and communicating with the mill, means for passing a stream'of heated" air through the e' mill and separator, ground material being carriedin suspension in the air stream upwardly from the mill into the separator and suiliciently pulverized material being carried from the separator in the air stream while insuillciently pulverized material vis rejected by the separator, means for collecting and withdrawing this rejected material comprising a rotating receptacle positioned in the path of the air stream intermediate the mill and separator and a scoop positioned to withdraw material collected on and thrown outwardly by the receptacle, and means for mixing a temporary binding agent with the withdrawn material and returning the mixture for further treatment by the grinding elements.

2. In combination, a mill comprising relatively moving grinding elements, means for feeding dry material to be ground into the mill, a separator above and communicating with the mill, means for passing a stream of heated air through the mill and separator, ground material being carried in suspension in the air stream upwardly from the mill into the separator and sufficiently pulverized material being carried from the separator in the air stream while insufliciently pulverized material is rejected by the separator, means for collecting and withdrawing this rejectedl material comprising a rotating receptacle positioned in the path of the air stream intermediate the mill and separator and a scoop positioned to withdraw material collected on and thrown outwardly by the receptacle, and means for mixing water with the withdrawn material and returning the mixture for further treatment between the grinding elements, the water being evaporated and carried out by the heated air stream.

3. In combination, a mill comprising relatively moving grinding elements, means for feeding dry material to be ground into the mill, a centrifugal separator communicating with the mill and comprising a rotating element adapted to concentrate the coarser material near the peripheral wall of the separator, means for passing a stream of heated air through the mill and separator, ground material being carried from the mill in suspension in the air stream and subjected to a centrifugal separating operation in the separator whereby the material requiring further grinding is concentrated near the peripheral wall of the separator, means comprising a scoop for withdrawing the insuiciently pulverized material from the separator, and means for mixing water with this withdrawn material and returning the mixture to the mill for further grinding, the Water being evaporated and carried out by the heated air stream.

4. In combination, a mill comprising relatively moving grinding elements, means for feeding dry materialto vbe ground into the mill, a separator communicating with the mill, means for passing a stream of 'heated air through the mill and separator, ground material being `carried in suspension in thel air-stream .from-.the mill intothe;

separator -suillcientlypulverized material be- .ing carried from the separator inthe air stream while material requiring further grinding is'rejected by the separator, means for selectively collecting and withdrawing different grades of material rejected from alternative positions in the separator and from the air stream Aintermediate the separator and mill, and means for mixing a temporary binding agent with the withdrawn material and returningthe mixture to the mill for further grinding.

5. In combination, a mill comprising relatively moving grinding elements, means for -feeding material to be'ground into the mill, a separator communicating with the mill, means for passing a stream of heated air through the mill and separator, ground material being carried in suspension in the air stream from the mill into the separator and sufficiently pulverized material being carried from the separator in the air stream while material requiring further grinding is rejected by the separator, means for selectively collecting and withdrawing dierent grades of material rejected from alternative positions in the separator and from the air stream intermediate the separator and mill, and means for mixing water with the withdrawn material and returning the mixture to the mill for further grinding, the water being evaporated and carried out by the heated air stream.

6. In combination, a mill comprising relatively movable grinding elements, means for feeding into the mill dry material to be ground, a separator communicating with the mill and comprising a peripheral wall, an inner rotating element and a centrifugal separating zone above said element and enclosed in the peripheral wall, means for passing a stream of heated air through the mill and separator, ground material being carried in suspension in the air stream from the mill into the separator and suiliciently pulverized material being carried from the separator in the air stream, some of the material requiring further grinding being concentrated in the peripheral portion of the centrifugal separating zone, a con'- duit leading from the peripheral wall of the separating zone, an adjustable scoop member positioned in the wall at the entrance to the conduit and adapted to withdraw the insuiliciently pulverized material from the air stream, a mixer into which the conduit leads, and means for feeding water into the mixer, the mixer delivering the mixture formed therein into the mill for further grinding, and the water being evaporated in the mill and carried out by the heated air stream.

'7. The process of pulverizing material which consists in first introducing solid and substantially dry material into a mill through which is passed a heated air stream which carries ground material from the mill in suspension, removing from the air stream insuiiiciently pulverized material which requires further grinding, subsequently removing from the air stream the suflciently pulverized material, mixing the rst removed insufleiently pulverized material with a temporary binding agent and introducing this mixture into the mill for further grinding, and removing the binding agent.

8. The process of pulverizing material which consists in rst introducing solid and substantially dry material into a mill through which is passed a heated air stream which carries ground material from the mill in suspension, removing.r

ciently pulverized material, mixing the flrst removed insuiliciently pulverized material with a temporary binding agent and introducing this' mixture into the mill for further grinding, and removing the binding agent in suspension in the air stream.

9. The process of pulverizing material which consists in rst introducing solid and substantially dry material into a mill through which is passed a heated air stream which carries ground material from the mill in suspension, removing `from the air stream insumciently pulverized material which requires further grinding, subsequently removing from. the air stream the sumciently pulverized material, mixing the rst removed insufiiciently pulverized material with a small quantity of water and introducing this coherent mixture into the mill for further grinding, the water'being evaporated and removed by the heated air stream.

'- JOE CRITES. 

